Abstract:To provide dynamic authorizations to users, access control must take into account context. Using this idea, we develop a Contextual Multi-Level Access Control Model based on Description Logic with Default and Exception named DL-CMLAC. To give a formal representation of this model, we define a non monotonic description logic based system by which we can deal with default and exceptional language called JClassic+. It is an extension of JClassic in order to introduce disjunction of concepts. JClassic+ is expressive enough to be of pratical use, it can handle a ”weakened kind of disjunction” with the connective lcs allowing a tractable subsumption computation. The connective lcs has the same properties as the LCS external operation to compute the least common subsumer of two concepts. Connectives of JClassic+ are used in a cleaver way to represent authorization in a default context, an exceptional context and composed context.